I
have wood lice. They prefer dark, moist places, reproduce
rapidly and scurry for shelter when exposed to light and heat.
I don’t mind these small critters in the least. Unlike other
lice you may be familiar with, these animals avoid the terrain
of the human body. They are important partners in my household
recycling efforts and critical contributors in the natural
decomposition processes that help keep our environment healthy.

You probably know wood lice by their more common name, “pill
bugs.” They are those small gray creatures that curl into
a ball like an armadillo when disturbed, and can often be
found in social gatherings beneath the shelter of damp decomposing
plant matter. They are particularly attracted to my compost
piles, where they rank right up there with earthworms as major
decomposers in converting my household garbage into rich soil.

While they are often referred to as bugs, these animals are
not insects. They are crustaceans, closely related to crabs,
lobsters, and shrimp. According to Paul Harding, a British
expert on pill bugs (and one of the few to report eating them),
these critters will not be joining their crustacean cousins
on the human menu due to a taste likened to “strong urine.”

While I refer to these animals as pill bugs, there are other
names used by American English speakers. The Dialect Survey
of the Harvard Department of Linguistics includes among its
questions, “What do you call the little gray creature that
rolls up into a ball when you touch it?” The top name, used
by a third of its over 10,000 respondents, was “roly poly,”
with “pill bug” coming in second with 16 percent, followed
by “potato bug” at 13 percent. Other names reported include:
sow bug, doodle bug, wood louse, basketball bug and twiddle
bug. Only 13 percent of respondents indicated that they did
not recognize the creature described.

The common pill bug is also known by the scientific name Armadillidium
vulgare, thanks to its body armor, which is made up of
seven plates that fit together to produce its armadillolike
defense against predators, like spiders and ants. Each of
these plates has a pair of legs (for a total of 14) that are
tucked under the crustacean’s body, making it seem to roll
along mechanically while its antenna flick about like erratic,
hyperactive windshield wipers.

Pill bugs are a type of crustacean known as “terrestrial isopods,”
which means that they live on land and have legs that are
all the same. They consume decaying organic matter, including
their own excrement. This behavior allows the animal to more
efficiently process material that has passed through its body.
Their life span averages about two years. They are not known
to harbor any human or plant diseases and are not known as
a crop pest. They do not bite or sting. There are thousands
of species of pill bugs loose on the planet today.

The ancient ancestors of pill bugs apparently used their substantial
set of legs to saunter out of the seas millions of years ago.
Before heading for land, they were probably bottom feeders,
munching on small bits of debris that settled to the ocean
floor. Among the oldest evidence for the creature’s move to
land are fossils frozen in amber that date back at least 35
million years. These fossils are so similar to today’s isopods
that it is reasonable to assume that their landing on shore
occurred much earlier than when these fossils were alive and
well.

Pill bugs retain a number of characteristics from their sea-dwelling
days. They have gills for breathing and their body coating
is permeable, requiring moist surroundings at around a 95-
percent humidity level to keep them from drying out. They
tend to bunch together in tight groups that appear to make
them quite social, but may actually be an important means
for these cold-blooded critters to cut down on their water
loss. It may also help sustain their high reproduction rates.
Females give birth to around 50 live young, which are nurtured
in a water-filled marsupiallike pouch until they emerge as
miniature adults. These terrestrial isopods also share with
their water-bound crustacean relatives a dependency on copper
to transport oxygen to their cells.

The pill bug, like the worm, was probably also a major contributor
to the development of soils and an atmosphere that fostered
the rich and diverse environment on this planet. Their role
in the breakdown of debris frees up needed nutrients to nurture
life, develops habitat for other soil-dwelling micro-recyclers,
and helps store carbon in the earth, reducing carbon dioxide
emissions into the atmosphere. The recycling behaviors of
these terrestrial isopods benefited life on this planet long
before humans evolved to take their first steps.

The species of pill bugs common in the United States today
are descendants of European imports. Research carried out
by the California Academy of Science mapped the genetic history
of these terrestrial isopods and found that the current species
of the creatures dominant in this country didn’t emerge from
the sea. They made their way across the Atlantic in wooden
ships. It is believed that the moist soil and rocks used as
ballast in the ships of European colonizers were ideal for
collecting and delivering the little critters to these shores.
The research found that pill bugs in the northeast states
were more closely related to those in the British Isles and
northern Europe, while those in the western United States
were genetically similar to those in Spain and southern Europe.

Regardless of where they came from, these simple little creatures
do amazing work in processing my household organic waste.
My compost heaps have become pill-bug high-rises, with growing
concentrations of the critters converging on their layers
of moist decomposing plant matter. These tiny animals continue
what their ancestors have done for millions of years: making
soil. In my backyard, thousands of gray crustaceans quietly
maintain this long-standing pursuit and I gratefully appreciate
their efforts.